The development and application of the miniaturization technology is the major trend of modern science. In particular, the integrated circuits (IC) and microelectromechanical systems (MEMS) technologies are the rudimentary methods of the microscopic world in the recent years. The world's smallest micro fan device in the world with dimension of 2 mm×2 mm (as shown in Appendix 1) is constructed by self-assembly micro blades and micro scratch drive actuators (SDAs). The SDA actuated micro fan is fabricated by using polysilicon based surface micromachining technology (multi-user MEMS processes, MUMPs) as Appendix 2 shows. An implemented micromotor chip is shown in Appendix 3.
Many researches and applications of SDA device have been reported in previous literatures. For instance, Terunobu Akiyama and his co-workers have first proposed the electrostatic controlled stepwise motion (i.e., scratch drive actuator) in polysilicon micro-slider, micro-motor and X/Y stage. As their experimental results show, the velocity of the microstructures is a function of applied pulse frequency and the step length is a function of the peak value of applied pulse and the length of SDA-plate. They also present a new basic reshaping technology to realize three dimensional silicon microstructures.
On the other hand, Ryan J. Linderman and Victor M. Bright proposed a novel MEMS-based micro rotary fan by using solder self-assembly and SDA technologies. Their papers demonstrated an electrostatically-driven MEMS rotary fan that can be further reduced in size and weight by bulk-etching the motor substrate—leaving only a thin structural layer to support the motor and fan blade array. The critical design aspects of SDA devices are the dimensions of the structural polysilicon layer, the bushing, the dielectric layer and the supporting beams. The optimized dimensions adopted in their micro-fan design are: a SDA-plate of 78 μm long by 65 μm wide, a bushing height of 1.5 μm; the 1.5 μm-thick supporting beams has 4 μm wide and 30 μm long.
The SDA micro rotary motor has been developed for more than one decade; however, such device has limited commercial applications due to its high driving voltage (30˜150 Vo-p). To overcome this disadvantage, this patent aims to develop a low driving voltage SDA micro motor using an ultra-low resistivity silicon wafer as chip substrate. A process has been developed which allows for photolithographically patterning a SDA micro motor formed on an ultra-low resistivity (<0.004 Ω-cm) silicon substrate. The ultra-low resistivity silicon substrate can reduce the driving voltage of SDA micro motor from 30˜150 Vo-p to 12˜30 Vo-p ac amplitude.
Another drawback of conventional SDA micro motor is its short lifetime. To improve this disadvantage, this invention presents a novel rib and flange structure design for lifetime enhancement, yield improvement and power reduction of SDA micro motor. A novel SDA micro motor with rib and flange structure designs has demonstrated a higher lifetime (>75 hrs) and rotational speed (˜30 rpm) in this patent.